Although woven fabrics have been successfully employed as backings for flexible coated abrasive products, such backings have not provided adequate performance in certain severe grinding operations. In these applications which require high strength of the load bearing member of the belt and retention of such high level of strength throughout the useful life of the abrasive coating thereon, the use of woven fabric backings has resulted at times in sudden dramatic and uncontrolled failure of belts, particularly when wide belts, that is over 24" in width, are employed in certain severe grinding operations. Another undesirable characteristic that often accompanies the use of woven fabrics as a backing in abrasive belting is puckering, which is believed to be caused by localized stretching of the belts when employed in severe grinding applications such as abrasive planing and machining. These undesirable characteristics appear to be inherent in woven fabric backed coated abrasive products including those in which the woven fabric is formed of polyester yarns.
These undesirable properties which appear to be inherent in woven fabric backed coated abrasive products can be mitigated by replacing the woven fabric with a straight warp fabric. For purposes of the present invention, a "straight warp fabric" is one that includes an array of warp yarns or cords that extend generally parallel to one another in a first plane joined to an array of weft yarns that extend generally parallel to one another in a second plane that is adjacent and parallel to the first plane. The weft yarns extend generally transversely of the warp yarns. The weft and warp yarns are joined to one another. This may be accomplished by a stitching yarn network. Alternatively, the warp and weft yarns may be joined to one another by adhesive bonding. The warp yarn array and the weft yarn array separately constitute individual planes that are parallel to one another. There is no interlacing of the warp and weft yarns with one another. The warp yarns all lay on one surface of the fabric and have no crimp in them, that is they lie in one plane. In similar manner, the weft yarns lie in one plane and have no crimp in them. Straight warp fabrics retain a significantly higher portion of theoretical strength of the yarns relative to a woven fabric formed on the same yarns and having the same count, that is the same number of yarns per unit dimension taken in the plane of the fabric and transversely to the lengthwise direction of the yarns or cords.
For purposes of the present invention, the term "yarn" is a generic term for a continuous strand of textile fibers, filaments or material in the form suitable for knitting, weaving or otherwise combining to form a textile fabric. The term "plied yarn" refers to the twisting together of two or more single yarns or plied yarns to form, respectively, plied yarn or cord. The term "cord" refers to the product formed by twisting together two or more plied yarns.
The terms "warp" and "weft" when used with respect to straight warp fabrics are not to be confused with their usage in conventional woven fabrics. For purposes of the present invention, the warp yarns or cords are those that extend in the machine direction during manufacture of the straight warp fabric, that is in the lengthwise direction of the fabric. This orientation is generally preserved when the fabric is employed as a backing for a coated abrasive product, such as belting; however, this need not be the case. The weft yarns generally extend across the warp yarns and form an angle of at least 45.degree. relative to the direction of the warp yarns.
While the invention will be described with respect to a straight warp fabric including a single array of warp yarns and a single array of weft yarns, it is to be understood that the use of a fabric including additional arrays of yarns, whether woven or not, is within contemplation of the invention. For purposes of the present invention, the term "straight warp fabric" also includes one that has inserted between arrays of straight yarns or attached to at least one array of straight yarns, a web of non-woven fabric. Such webs are produced by well known techniques and include spun-bonded and stitch-bonded fabrics. The use of a non-woven web insert in a straight warp fabric increases the available surface area for coating resins and latexes thereby improving adhesion of the components of the backing to one another and to subsequently applied coatings including the abrasive grain material. The incorporation of a non-woven web assists in controlling placement of the cloth finishing mixes. The presence of such non-woven web additionally increases the resistance to tearing of the flexible sheet material as well as providing additional cover.
Straight warp fabrics tend to be or may be of a more open construction than conventional woven cloth of the same design strength. This greater openness requires employment of different coating materials and techniques to fill in the interstices that exist between the adjacent yarns of each array in such straight warp fabrics in their greige state. The term "greige" as applied to fabrics for purposes of the present invention refers to the fabric in the state it exists as received from the machine on which it was formed. In the case of a straight warp fabric, a greige fabric is one delivered to or taken from the wind-up stand of the straight warp fabric forming machine. The present invention is particularly directed to such techniques and materials to provide a flexible sheet material that is highly stable and durable when used as a backing for coated abrasive products when compared to conventional woven cloth backings formed from yarns or cords of identical construction and count.